Shelf Surface Waters Research Articles

First assessment of microplastic and artificial microfiber contamination in surface waters of the Amazon Continental Shelf

The composition and distribution of microplastics (MPs) in the Brazilian Amazon Continental Shelf surface waters are described for the first time. The study was conducted during the 2018 rainy and dry seasons, using 57 water samples collected with aluminum buckets and filtered through a 64-μm mesh. The samples were vacuum-filtered in a still-air box, and the content of each filter was measured, counted, and classified. A total of 12,288 floating MPs were retrieved; particles were present at all 57 sampling points. The mean MP abundance was 3593 ± 2264 items·m−3, with significantly higher values during the rainy season (1500 to 12,967; 4772 ± 2761 items·m−3) than in the dry season (323 to 5733; 2672 ± 1167 items·m−3). Polyamides (PA), polyurethane (PU), and acrylonitrile butadiene styrene (ABS) were the most common polymers identified through Fourier Transform Infrared Spectroscopy (FTIR) analysis. Cellulose-based textile fibers were also abundant (~40%). Our results indicate that the Amazon Continental Shelf is contaminated with moderate to high levels of MPs; the highest abundances were recorded at stations near land-based sources such as river mouths and large coastal cities.

Analysis of Iron Sources in Antarctic Continental Shelf Waters

AbstractPrevious studies showed that satellite‐derived estimates of chlorophyll a in coastal polynyas over the Antarctic continental shelf are correlated with the basal melt rate of adjacent ice shelves. A 5‐km resolution ocean/sea ice/ice shelf model of the Southern Ocean is used to examine mechanisms that supply the limiting micronutrient iron to Antarctic continental shelf surface waters. Four sources of dissolved iron are simulated with independent tracers, assumptions about the source iron concentration for each tracer, and an idealized summer biological uptake. Iron from ice shelf melt provides about 6% of the total dissolved iron in surface waters. The contribution from deep sources of iron on the shelf (sediments and Circumpolar Deep Water) is much larger at 71%. The relative contribution of dissolved iron supply from basal melt driven overturning circulation within ice shelf cavities is heterogeneous around Antarctica, but at some locations, such as the Amundsen Sea, it is the primary mechanism for transporting deep dissolved iron to the surface. Correlations between satellite chlorophyll a in coastal polynyas around Antarctica and simulated dissolved iron confirm the previous suggestion that productivity of the polynyas is linked to the basal melt of adjacent ice shelves. This correlation is the result of upward advection or mixing of iron‐rich deep waters due to circulation changes driven by ice shelf melt, rather than a direct influence of iron released from melting ice shelves. This dependence highlights the potential vulnerability of coastal Antarctic ecosystems to changes in ice shelf basal melt rates.

Mechanism of formation, mineralogy and geochemistry of the ooidal ironstone of Djebel Had, northeast Algeria

The Djebel Had Ironstone (DHIS), an 8 m thick stratiform sedimentary iron formation, forms part of the important mining district of south Tebessa, in northeastern Algeria. Stratigraphic, lithological, structural and metallogenic similarities, suggest the DHIS may extend further into southwestern Tunisia. We show that mineralization occurs as layers of ooidal ironstones and inter-laminated iron marl within mid-Eocene gypsiferous marls. The more or less rounded 0.1–2.0 mm brownish-blackish ooids, are composed of goethite, limonite, hematite, with traces of magnetite and piemontite. The grains display a smooth outer surface bound by an argilo-ferruginous layer embedded in siliceous-calcite cement. They are unusually friable, crumbling at the slightest shock. A high total iron (FeT) content of 50.12%, is dominated by up to 71.06% iron hydroxide (FeO(OH). Much of the iron is present as goethite, a common feature of iron-rich ooids of North African origin. However, the lack of prominent chlorite minerals suggest the DHIS is not of a detrital origin. Instead, a negligible Ti and Al oxide concentration suggest a chemical provenance for the DHIS. The data suggest that ferruginous conditions developed in a potentially restricted/semi-restricted continental shelf margin where seafloor redox was sensitive to the alternating cycles of sea level change. We propose a new mechanism for the formation of ooidal ironstones, associated with shelf surface water eutrophication, bottom water anoxia promoted by sea level rise and the weathering of iron phosphate-rich rocks. Phosphorus and cerium enrichment, coupled to reconstructed redox depositional conditions and sediment mineralogy, suggest that intense biomass production stimulated the deoxygenation of shelf bottom waters and the deposition of the DHIS beneath a ferruginous water column.

Gulf Stream Ring Water Intrusion on the Mid-Atlantic Bight Continental Shelf Break Affects Microbially Driven Carbon Cycling

Warm core, anticyclonic rings that spin off from the Gulf Stream circulate through the region directly offshore of the Mid-Atlantic Bight. If a warm core ring reaches the continental shelf break, its warm, highly saline water may subduct under cooler, fresher continental shelf surface water, resulting in subsurface waters at the shelf break and over the upper continental slope with high temperatures and salinities and distinct physical and chemical properties characteristic of Gulf Stream water. Such intruding water may also have microbial communities with distinct functional capacities, which may in turn affect the rate and nature of carbon cycling in this coastal/shelf environment. However, the functional capabilities of microbial communities within ring intrusion waters relative to surrounding continental shelf waters are largely unexplored. We investigated microbial community capacity to initiate organic matter remineralization by measuring hydrolysis of a suite of polysaccharide, peptide, and glucose substrates along a transect oriented across the Mid-Atlantic Bight shelf, shelf break, and upper slope. At the outermost sampling site, warm and salty water derived from a Gulf Stream warm core ring was present in the lower portion of the water column. This water exhibited hydrolytic capacities distinct from other sampling sites, and exhibited lower heterotrophic bacterial productivity overall. Warm core rings adjacent to the Mid-Atlantic Bight shelf have increased in frequency and duration in recent years. As the influence of warm core rings on the continental shelf and slope increases in the future, the rate and nature of organic matter remineralization on the continental shelf may also shift.

Elemental composition of suspended particles across the southeastern continental shelf off the coast of North Florida and South Georgia: Provenance, transport, fate and implications to mid-outer shelf water column processes.

This paper reports on the chemistry of suspended particulates collected in waters of the southeastern US continental shelf off the coasts of North Florida and South Georgia. Approximately 350 suspended sediment samples were analyzed for particulate organic carbon and nitrogen (POC and PON), particulate aluminum and calcium and a suite of trace metals which included particulate alkaline earths (magnesium, strontium, barium), particulate rare earth metals (lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium and dysprosium), particulate transition metals (cobalt, copper, iron, manganese, nickel. scandium, titanium and vanadium) and others: particulate cadmium, zinc, thorium and uranium. The samples were collected in the fall of 1987 during a multidiscipline expedition (FLEX) focused on cross shelf exchange of water and materials during northward wind stress and fall Gulf Stream intrusions. Although samples were analyzed shortly after collection, archived data have not been previously presented. Results are interpreted with regard to how they relate to particle provenance, transport and fate.Results indicate that significant influence of terrestrial sources of suspended particles is limited to the inner shelf, however the concentrations of some metals, such as rare earths, appear to reflect this provenance across the entire shelf. Mid-outer shelf particles are dominated by re-suspended biogenic carbonates and biogenic organic carbon rich particles formed in response to Gulf Stream up welled nutrients. Particulate trace element concentrations and primary production in mid-outer shelf waters are interpreted as a response to not only nutrient, but also trace metal enrichment of up welled Gulf Stream water intruded onto the shelf. Based on particle chemistry, micro nutrients such as Fe in upwelled waters may be limiting in sustaining mid-outer shelf production. Other trace metals such as Sc appear to be enriched due to adsorption on organic rich particles. And the formation SrSO4 particles, originating from Acantharian spicules, appear to create an environment for the precipitation of barite in outer shelf surface waters.

Leucine, starch and bicarbonate utilization by specific bacterial groups in surface shelf waters off Galicia (NW Spain).

The capability of different bacterial populations to degrade abundant polymers, such as algal-derived polysaccharides, or to utilize preferentially polymers over monomers, remains largely unknown. In this study, microautoradiography was combined with fluorescence in situ hybridization (MAR-FISH) to evaluate the ability of Bacteroidetes, SAR11, Roseobacter spp., Gammaproteobacteria and SAR86 cells to use bicarbonate, leucine and starch under natural light conditions at two locations in shelf surface waters off NW Spain. The percentage of cells incorporating bicarbonate was relatively high (mean 32% ± 4%) and was positively correlated with the intensity of solar radiation. The proportion of cells using starch (mean 56% ± 4%) or leucine (mean 47% ± 4%) was significantly higher than that using bicarbonate. On average, SAR11, Roseobacter spp. and Gammaproteobacteria showed a similarly high percentage of cells using leucine (47%-65% of hybridized cells) than using starch (51%-64% of hybridized cells), while Bacteroidetes and SAR86 cells preferentially used starch (53% of hybridized cells) over leucine (34%-40% of hybridized cells). We suggest that the great percentage of bacteria using starch is related to a high ambient availability of polymers associated to algal cell lysis, which, in turn, weakens the short-term coupling between phytoplankton release and bacterial production.

The distribution and inter-annual variation of water masses on the Bering Sea shelf in summer

On the basis of the CTD data obtained within the Bering Sea shelf by the Second to Sixth Chinese National Arctic Research Expedition in the summers of 2003, 2008, 2010, 2012 and 2014, the classification and interannual variation of water masses on the central Bering Sea shelf and the northern Bering Sea shelf are analyzed. The results indicate that there are both connection and difference between two regions in hydrological features. On the central Bering Sea shelf, there are mainly four types of water masses distribute orderly from the slope to the coast of Alaska: Bering Slope Current Water (BSCW), MW (Mixed Water), Bering Shelf Water (BSW) and Alaska Coastal Water (ACW). In summer, BSW can be divided into Bering Shelf Surface Water (BSW_S) and Bering Shelf Cold Water (BSW_C). On the northern Bering Sea shelf near the Bering Strait, it contains Anadyr Water (AW), BSW and ACW from west to east. But the spatial-temporal features are also remarkable in each region. On the central shelf, the BSCW is saltiest and occupies the west of 177°W, which has the highest salinity in 2014. The BSW_C is the coldest water mass and warmest in 2014; the ACW is freshest and mainly occupies the east of 170°W, which has the highest temperature and salinity in 2012. On the northern Bering Sea shelf near the Bering Strait, the AW is saltiest with temperature decreasing sharply compared with BSCW on the central shelf. In the process of moving northward to the Bering Strait, the AW demonstrates a trend of eastward expansion. The ACW is freshest but saltier than the ACW on the central shelf, which is usually located above the BSW and is saltiest in 2014. The BSW distributes between the AW and the ACW and coldest in 2012, but the cold water of the BSW_C on the central shelf, whose temperature less than 0°C, does not exist on the northern shelf. Although there are so many changes, the respond to a climate change is synchronized in the both regions, which can be divided into the warm years (2003 and 2014) and cold years (2008, 2010 and 2012). The year of 2014 may be a new beginning of warm period.

Post-bomb coral Δ14C record from Iki Island, Japan: possible evidence of oceanographic conditions on the northern East China Sea shelf

In this study, a sea-surface water Δ14C record of AD 1966–2000 (i.e., after the atmospheric nuclear-bomb testing period of the mid-1950s to early 1960s) was reconstructed from a coral sample collected from Iki Island, western Japan. The island is located in the Tsushima Strait where the Tsushima Current flows from the East China Sea (ECS) continental shelf into the Sea of Japan, indicating a strong influence of the ECS shelf water on the island. It is widely accepted that the Tsushima Current originates in the area between the ECS shelf break and the Nansei Islands further offshore as a branch of the Kuroshio Current, although another possible origin is the Taiwan–Tsushima Current System. The Δ14C record from Iki Island shows the following evidence of a response to the atmospheric nuclear testing: (1) an increase from ~55‰ in 1966 to ~133‰ in 1970, (2) a plateau ranging between ~123 and ~142‰ during the 1970s to the late 1980s, and (3) a gradual decrease from ~115‰ in 1990 to ~83‰ in 2000. Comparison of this record with coral Δ14C records from the Nansei Islands (Okinawa Island, Ishigaki Island and Kikai Island), located ~160–280 km off the ECS shelf break and little influenced by the shelf water, suggests that the surface-water Δ14C around Iki Island was ~30–45‰ lower than that of the Nansei Islands from the mid-1960s to late 1970s, and that the Δ14C difference between Iki Island and the Nansei Islands decreased from the end of the 1970s to ~0–15‰ in the mid-1980s to 2000. The lower Δ14C around Iki Island can be explained as follows: (1) in contrast to the Nansei Islands area, the ECS shelf area is a vertically mixed, highly concentrated carbon reservoir significantly connected to subsurface and deeper waters outside the shelf area, strongly suggesting that the surface-water Δ14C of the shelf area (perhaps excepting very shallow innermost shelf areas) was significantly less sensitive to the atmospheric nuclear-bomb 14C spike than that of the Nansei Islands area; (2) the shelf-surface water is conveyed from the northern ECS to Iki Island by the Tsushima Current. Thus, it can be suggested that the post-bomb coral Δ14C record from Iki Island reflects oceanographic conditions of the northern ECS shelf.

Temporal and spatial variations of dissolved and colloidal trace elements in Louisiana Shelf waters

Selected trace elements (TEs), dissolved organic carbon and nutrients were studied in Louisiana Shelf waters including the low salinity Mississippi (MR) and Atchafalaya (AR) River plumes during periods of high, intermediate and low river discharge in 2008–2009. The dissolved phase (<0.02μm) was predominant for Cs, Cu, Mo, Ni, and U, while Fe was mainly in the colloidal phase (0.02–0.4μm). Cobalt, Cr and Mn existed mainly in the dissolved phase but sometimes showed significant colloidal concentrations in low (Cr, Mn) and middle (Co) salinity. In the shelf surface waters, dissolved Cs, Cu, Mo, Ni, and U showed conservative as well as non-conservative behaviors relative to salinity gradients, with vertical mixing the main cause for apparent non-conservative behavior. However, the other TEs showed consistently non-conservative behavior during all sampling campaigns. Through examination of associated mixing experiments, nutrient and chlorophyll distributions, and surface-bottom concentration contrasts, the non-conservative behavior of TEs was variously related to colloidal flocculation (Fe, Cr), biological activity (Fe, Mn), desorption (Co), photochemical reaction (Cr) and benthic mobilization (Co, Cu, Ni, Mn). During the June/July 2009 bottom hypoxia season, TE concentrations in bottom waters were greatly enriched (Co, Cu, Ni, Mn, Fe) and depleted (Cr, V), probably due to particulate or sedimentary dissolution and/or diffusion for the enrichment, and diffusion into sediment and/or adsorptive removal onto particles for the depletion under prolonged reducing conditions. We also observed seasonal variations of TEs and nutrients in the two river plumes as well as in shelf waters. These seasonal variations appear to be related to the variation of mixing ratios of MR tributaries for the MR plume as well as inputs from the Red River and wetlands in the Atchafalaya Basin for the AR plume and contribute to observed variability of shelf TE distributions. More importantly, evidence of considerable vertical mixing, even during strong stratification associated with bottom water hypoxia, suggests that vertical mixing of bottom recycled nutrients may be an important mechanism for sustaining shelf biological production. Bottom-enriched (or depleted) TEs and nutrients that are not mixed upwards likely flow off the shelf delivering these materials offshore to the open Gulf of Mexico. Given the predicted rapid growth of coastal eutrophication and bottom water hypoxia under current global climate change scenarios, a better understanding of these recycled vertical and offshore fluxes is required for proper implementation in modeling studies and management strategies.

Ecophysiology of picophytoplankton in different water masses of the northern Bering Sea

Picophytoplankton are important primary producers in oligotrophic waters and sensitive to environmental changes. However, little is known about their ecophysiology in the northern Bering Sea with complex water masses. The distribution of picophytoplankton with their optical physiological features and physicochemical characteristics as well as water masses were investigated on the northern Bering Sea Shelf during the summer of 2008. Flow cytometry and statistical analysis including Pearson correlation analysis and cluster analysis were the main methods used. Synechococcus and picoeukaryotes were the primary existing picophytoplankton assemblages, with their respective abundances ranging from 0 to 2.69 × 106 and 0.47 × 106 to 13.20 × 106 cells l−1 and peaking at water depths of 10–30 m with surface light levels of 30–50 %. Larger Synechococcus cells contained larger amounts of chlorophyll a (Chl a) and phycoerythrin. Low temperature, high nutrient concentrations and a high N/P value (>7) might limit cell abundance of picoeukaryotes, as shown by their close relationships. With an increase of temperature and oligotrophic freshwater input, smaller picophytoplankton would thrive and the cellular Chl a (Chl a/cell) increase with higher contribution to total Chl a. Seven water types with different physicochemical and biological characteristics were differentiated using the mini-ecosystem (a descriptor of a composite of parameters defining a composite water type community, including temperature, salinity, macronutrients and community abundance of picophytoplankton) as an indicator. They are Alaska Coastal Water, Bering Shelf Surface Water, 20–40 m of Bering Shelf Water, Bering Shelf Cold Water, Anadyr Water, Anadyr-Bering Shelf Water (Bering Sea Water) and Cold Pool.

Dynamics and stoichiometry of nutrients and phytoplankton in waters influenced by the oxygen minimum zone in the eastern tropical Pacific

The tropical South East Pacific is characterized by strong coastal upwelling on the narrow continental shelf and an intense oxygen minimum zone (OMZ) in the intermediate water layer. These hydrographic properties are responsible for a permanent supply of intermediate water masses to the surface rich in nutrients and with a remarkably low inorganic N:P stoichiometry. To investigate the impact of OMZ-influenced upwelling waters on phytoplankton growth, elemental and taxonomical composition we measured hydrographic and biogeochemical parameters along an east–west transect at 10°S in the tropical South East Pacific, stretching from the upwelling region above the narrow continental shelf to the well-stratified oceanic section of the eastern boundary regime. New production in the area of coastal upwelling was driven by large-sized phytoplankton (e.g. diatoms) with generally low N:P ratios (<16:1). While nitrate and phosphate concentrations were at levels not limiting phytoplankton growth along the entire transect, silicate depletion prohibited diatom growth further off-shore. A deep chlorophyll a maximum consisting of pico-/nano- (Synechococcus, flagellates) and microphytoplankton occurred within a pronounced thermocline in subsurface waters above the shelf break and showed intermediate N:P ratios close to Redfield proportions. High PON:POP (>20:1) ratios were observed in the stratified open ocean section of the transect, coinciding with the abundance of two strains of the pico-cyanobacterium Prochlorococcus; a high-light adapted strain in the surface layer and a low-light adapted strain occurring along the oxic-anoxic transition zone below the thermocline. Excess phosphate present along the entire transect did not appear to stimulate growth of nitrogen-fixing phytoplankton, as pigment fingerprinting did not indicate the presence of diazotrophic cyanobacteria at any of our sampling stations. Instead, a large fraction of the excess phosphate generated within the oxygen minimum zone was consumed by non-Redfield production of large phytoplankton in shelf surface waters.

Fluorescence: Absorption coefficient ratio — Tracing photochemical and microbial degradation processes affecting coloured dissolved organic matter in a coastal system

The optical properties of coloured dissolved organic matter (CDOM) – absorption coefficient, induced fluorescence, and fluorescence quantum yield – were determined in the coastal eutrophic system of the Ría de Vigo (NW Spain) under two contrasting situations: a downwelling event in September 2006 and an upwelling event in June 2007. Significantly different optical properties were recorded in the shelf surface (higher absorption coefficient and lower quantum yield) and bottom (lower absorption coefficient and higher quantum yield) waters that entered the embayment during downwelling and upwelling conditions, respectively. Continental waters presented distinctly high CDOM levels. The spatial and temporal variability of the induced fluorescence to absorption coefficient ratio during the mixing of shelf and continental waters was used to quantify the relative importance of photochemical and microbial processes under these contrasting hydrographic conditions. Photochemical processes were dominant during the downwelling episode: 86% of the variability of CDOM can be explained by photochemical degradation. On the contrary, microbial processes prevailed during the upwelling event: 77% of the total variability of CDOM was explained by microbial respiration.

Seasonal and event-controlled export of organic matter from the shelf towards the Gulf of Lions continental slope

To investigate the role of coastal canyons in the transfer of organic matter from the shelf to the slope and basin, we deployed sediment trap/current meter pairs at the head of five canyons in the Gulf of Lions (GoL) between November 2003 and May 2004. Analysis of organic carbon, biogenic silica, Corg isotopic composition, Corg/total nitrogen, chloropigments, and amino acids clearly shows the seasonal influence and effect of extreme meteorological events on the composition of collected particles. The sampling period was divided into three “scenarios”. The first corresponded to a large easterly storm and flood of the Rhone river during stratified water column conditions; the composition of material collected during this event was influenced by increased transfer of riverine and coastal particulate matter, with a lower Corg content. During the second “fall-winter” scenario, northern and northwestern winds blowing over the shelf caused cooling and homogenization of the shelf water column; particles collected at this time reflected the homogeneous source of particulate matter transported through canyons; particles sitting in the vicinity of canyon heads are most likely swept downslope by the general south-westward circulation. Organic tracers indicate a degraded origin for organic matter transported during this period. A third “spring” scenario corresponded to northern winds alternating with eastward windstorms that triggered and/or enhanced the cascading of dense waters accumulated on the bottom of the shelf due to previous cooling. These conditions occurred in conjunction with increased phytoplankton productivity in shelf surface waters. Organic matter advected mainly by dense shelf water cascading was fresher due to the transport of newly produced particles and a variable terrestrial fraction; this fraction depended on the proportion of resuspended material accumulated during previous high discharge periods that was involved in each transport pulse. The tight link shown between meteorological conditions and organic matter transport is important for continental margin geochemical studies as future changes in climatic conditions may lead to dramatic changes in carbon sequestration capability and in the ecosystems of deep margin environments.

Nutrient and organic matter patterns across the Mackenzie River, estuary and shelf during the seasonal recession of sea-ice

Suspended material, nutrients and organic matter in Mackenzie River water were tracked along a 300 km transect from Inuvik (Northwest Territories, Canada), across the estuarine salinity gradient in Kugmallit Bay, to offshore marine stations on the adjacent Mackenzie Shelf. All particulates measured (SPM, POC, PN, PP) declined by 87–95% across the salinity gradient and levels were generally below conservative mixing. Organic carbon content of suspended material decreased from 3.1% in the river to 1.7% in shelf surface waters while particulate C:N concurrently decreased from 17.1 to 8.6. Nitrate and silicate concentrations declined by more than 90% across the salinity gradient, with nitrate concentrations often below the conservative mixing line. Phosphate concentrations increased from 0.03 μmol/L in the river to 0.27 μmol/L over shelf waters, thereby changing the inorganic nutrient regime downstream from P to N limitation. Dissolved organic carbon decreased conservatively offshore while dissolved organic N and P persisted at high levels in the Mackenzie plume relative to river water, increasing 2.7 and 25.3 times respectively. A deep chlorophyll- a maximum was observed at two offshore stations and showed increases in most nutrients, particulates and organic matter relative to the rest of the water column. During river passage through the Mackenzie estuary, particulate matter, dissolved organic carbon and inorganic nutrients showed sedimentation, dilution and biological uptake patterns common to other arctic and non-arctic estuaries. Alternatively, inorganic content of particles increased offshore and dissolved organic N and P increased substantially over the shelf, reaching concentrations among the highest reported for the Arctic Ocean. These observations are consistent with the presence of a remnant ice-constrained (‘stamukhi’) lake from the freshet period and a slow flushing river plume constrained by sea-ice in close proximity to shore. Nutrient limitation in surface shelf waters during the ARDEX cruise contributed to the striking deep chlorophyll- a maximum at 21 m where phytoplankton communities congregated at the margin of nutrient-rich deep ocean waters.

Bacterioplankton community composition in nearshore waters of the NW Black Sea during consecutive diatom and coccolithophorid blooms

In this study we analyzed the dynamics of bacterioplankton community composition during coastal Black Sea phytoplankton blooms using a combination of whole-cell fluorescence in situ hybridization with rRNA-targeted oligonucleotide probes and catalyzed reporter deposition (CARD-FISH). Bacterial and algal assemblages were sampled in eutrophic shelf surface waters in Constanta Bay between May and August 2004. While diatoms dominated the spring phytoplankton bloom, the late summer bloom (16-August) involved mainly coccolithophorids and dinoflagellates. The coccolithophorid Emiliania huxleyi was the numerically abundant phytoplankton species in August (~1.1 × 106 cells/L). The composition of bacterioplanktonic communities was dominated by members of alpha-Proteobacteria (mainly the Roseobacter clade) and gamma-Proteobacteria, which together accounted for up to 31% of total prokaryotic abundance during the summer phytoplankton bloom. Our results suggest that members of gamma-Proteobacteria and the Roseobacter clade are associated with Emiliania huxleyi blooms in the Black Sea.

The genus Pseudo- nitzschia (Bacillariophyceae) in continental shelf waters of Argentina (Southwestern Atlantic Ocean, 38–55°S)

The distribution pattern of Pseudo- nitzschia species, associated phytoplankton flora and its relationships with main environmental factors were studied for the first time in continental shelf surface waters of the Argentine Sea (Southwestern Atlantic Ocean, 38–55°S). Both qualitative and quantitative samples, collected during summer and fall 2003, were examined using light and scanning electron microscopy. Results indicated that the genus Pseudo- nitzschia has a wide distribution along the studied area. It was present at low densities, with infrequent peak abundances and appeared most frequently as a minor component of the diatom populations that typically develop on the continental shelf of the Argentine Sea. Moreover, phytoplankton communities were numerically dominated by unidentified phytoflagellates (≤5 μm) throughout almost all samples analyzed. Eight Pseudo- nitzschia species were identified in our study: P. australis, P. fraudulenta, P. heimii, P. lineola, P. pungens, P. cf. subcurvata, P. turgidula and P. turgiduloides. Of these, P. heimii, P. lineola and P. turgiduloides are new records for the Argentine Sea. Their presence in the area is attributable to the influence of southerly cold water masses. Spatial and temporal variations of the environmental parameters recorded in the study area generally determined the distribution of Pseudo- nitzschia species. P. pungens and P. australis were widely distributed and reached high densities, especially in waters with elevated temperatures and salinities (around 15 °C, 33.8 psu) and low nutrients concentrations. On the other hand, P. heimii, P. lineola, P. turgidula and P. turgiduloides showed a more restricted distribution, with lower densities in relatively cold, less saline (8 °C, 32.45 psu) and nutrient-rich waters. From the Pseudo- nitzschia species found throughout this survey, P. australis, P. fraudulenta, P. pungens and P. turgidula are known as domoic acid (DA) producers around the world, but there is little information on the potential toxicity of these species in Argentina.

Cohort Dynamics of Summer‐Spawned Bluefish as Determined by Length‐Frequency and Otolith Microstructure Analyses

AbstractElucidating recruitment processes in marine fish is difficult when species occupy distinct habitats at different ontogenetic stages and when multiple cohorts determine year‐class strength. Currently, there is insufficient information on the cohort dynamics of the early life history stages of summer‐spawned bluefish Pomatomus saltatrix to critically evaluate each cohort's role in regulating population dynamics. The objective of this study was to provide greater insight into the cohort dynamics of summer‐spawned bluefish during the summer and fall on the inner continental shelf off southern New Jersey. Length‐frequency and otolith microstructure analyses were used to estimate the age, hatch date, and growth of neustonic individuals collected from shelf surface waters during August–October 1998. Bluefish ranged between 9 and 46 d in age, corresponding to back‐calculated hatch dates between 27 June and 13 September. Hatch date frequencies were decomposed into a series of normal curves and identified three cohorts with mean hatch dates occurring in early July (cohort 1), late July to early August (cohort 2), and late August to early September (cohort 3). Cohort‐specific growth rates ranged between 0.28 and 0.81 mm standard length/d. Otolith microstructure analysis revealed that growth was significantly faster for cohort 1 than for the other cohorts, most likely because of spatial and temporal variability in the environment (e.g., temperature) and size‐selective processes (e.g., mortality). Back‐calculated spawning dates indicated that the functional spawning output of bluefish was significantly greater during the first‐quarter phase of the lunar cycle. Collectively, these observations suggest that the cohort structure of bluefish is more complex than previously recognized.

Phosphorus speciation and budget of the East China Sea

Water samples collected from the inner (<50 m), middle (50–200 m) and outer (>200 m) shelves of the East China Sea (ECS) were analyzed to investigate the importance of dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate inorganic phosphorus (PIP) in the water column. Concentrations of DIP, DOP and PIP ranged 0.05–3.01 μM, 0.01–0.54 μM and 0.18–13.94 ı̀mol g −1, respectively. Higher values were generally found in the inner shelf. Significantly higher concentrations of suspended particulate matter (SPM) (mean value 16.87 mg l −1) and PIP (mean value 11.59 μmol g −1) were found near the bottom along the inner shelf and was attributed to re-suspension of sediments. DIP was the major form of dissolved P, accounting for more than 70% of the total dissolved P (TDP) pool in inner and middle shelf waters. However, the DOP concentration generally exceeded the DIP concentration in the surface layer (<100 m) of the outer shelf. PIP was 10–20% of the total P pool (TDP+PIP) in the inner shelf and decreased markedly to less than 1% in the outer shelf. It was also found that the higher the concentrations of SPM and of particulate iron, the higher the percentage of P bound by particles. The phosphorus budget on the ECS was also calculated by employing a box model based on the balance of the water mass and phosphorus mass. The model results revealed that the Kuroshio Surface Water, the Kuroshio Tropical Water, the Kuroshio Intermediate Water and the Taiwan Strait Water annually import approximately 8.6±5.7×10 9 mol, 6.7±5.6×10 9 mol, 28.9±22.2×10 9 mol, and 22.8±13×10 9 mol P, respectively, into the ECS. These imports of P are primarily transported in the dissolved phase. In contrast, the input of P, 11.8±2.3×10 9 mol P yr −1, from the Changjiang River is chiefly transported in the solid phase. The Shelf Surface Water annually exports 44.5±27.3×10 9 mol P out of the ECS, predominately in the dissolved phase. The ECS is a phosphorus sink with approximately 34.3±21.5×10 9 mol P yr −1 deposited in the sediments. Finally, the results of the present study suggested that PIP and DOP could not be ignored when studying the geochemistry of P in the inner and outer shelf, respectively, of the ECS.

Late Pleistocene–Holocene oceanographic variability in the Okhotsk Sea: geochemical, lithological and paleontological evidence

Sedimentary, geochemical and paleontological data, extracted from a sediment core taken from the central Okhotsk Sea, record climatic and sedimentary changes over the past 100 ky. Benthic foraminiferal oxygen isotope record and accelerator mass spectrometry (AMS) 14C data provide the basis for the core age chronology. Planktonic and benthic foraminiferal δ 18O and δ 13C measurements, magnetic susceptibility, ice rafted debris and coarse fraction content, carbonate and organic carbon content, and diatom and pollen spectra show major changes in regional climate, sea surface conditions, ice extent and sedimentary regime, which are correlated with the global glacial–interglacial changes of marine isotope stages (MIS) 1 through 5.3. Regional cooling and intensification of winter sea ice formation during the last glaciation increased the northern shelf surface water density and Sea of Okhotsk Intermediate Water (SOIW) formation. In addition to major Milankovitch-scale changes, lithological, geochemical and paleontological indices also show suborbital oscillations in Okhotsk Sea hydrology, sedimentation and regional climate. These shorter-term oscillations are characterized by coupled maxima in ice rafted debris and sediment coarse fraction (lithodynamic indices, LDI) values and most are associated with cold events involving enhanced winter ice formation and intensification of SOIW and North Pacific intermediate water (NPIW) formation. The terminations of LDI maxima were induced by climate warming and reductions in ice formation, and were accompanied by sharp decreases in planktonic foraminiferal δ 18O. During the glacial terminations of MIS 2 and 4, however, the onset of suborbital-scale LDI maxima occurs close to sharp negative δ 18O shifts in planktonic foraminifera ( δ 18Opf) associated with climate warming. In these special cases, the LDI maxima occurred under warm climate and rising sea levels and did not lead to increases in SOIW or NPIW ventilation.

Analysis of apparent optical properties and ocean color models using measurements of seawater constituents in New England continental shelf surface waters

We used budgets of absorption (a), scattering (b), and backscattering (bb) for particles and chromophoric dissolved organic matter (CDOM) to investigate sources of seasonal variations in apparent optical properties (AOPs) of New England continental shelf surface waters. Spectral a, b, and bb budgets for particles were estimated from flow cytometric measurements of eukaryotic pico/nanophytoplankton, Synechococcus, heterotrophic prokaryotes, detritus, and minerals; AOPs were modeled with Hydrolight radiative transfer software. For late summer and spring, our modeled values of the diffuse attenuation coefficient (Kd) and remote sensing reflectance (Rrs) were on average within 15% and 9%, respectively, of independent measurements. This close agreement allowed us to examine how different seawater constituents contributed to AOP variability. Higher values of Kd in the spring, compared to summer, were due to higher absorption by eukaryotic phytoplankton (aeuk) and CDOM (aCDOM), which coincided with higher nutrient levels and less stratified conditions than in the summer. Differences in the spectral shape of Rrs between the seasons were caused by a combination of differences in aeuk, aCDOM, and bb from non‐phytoplankton particles (minerals and detritus combined). For non‐phytoplankton bb the major seasonal difference was a higher inverse wavelength dependence in the summer due to the effects of small organic detritus. We applied two semianalytical ocean color models to our data, in order to evaluate whether the assumptions and parameterizations inherent in these models are applicable for New England shelf waters. We show how differences between observed and modeled chlorophyll a specific phytoplankton absorption, aCDOM, and non‐phytoplankton bb cause errors in chlorophyll a concentration and IOPs retrieved from reflectance inversion models.